Robotic arms are increasingly used in a number of different applications, from manufacturing, to servicing, and assistive robotics, among numerous possibilities. Serial robot arms are convenient in that they cover wide working volumes. Standard topology of mechanical brakes for actuators of robot arms, such as serial robot arms, typically consists of a motor module, a gear module and a mechanical brake module. Such topology requires that these modules be stacked up in a way that the volume and the weight of the actuator are respectively large and heavy, and therefore inefficient for robotic arm actuators. For instance, serial robot arms must support their one weight, and the prior-art topology may thus need improvements.